In the development of hepatocellular carcinoma, a new population of cells or a progenitor cell appears and undergoes a series of changes which ultimately form neoplasia. During their evolution into carcinomas, the discrete cells or cell populations acquire phenotypic properties different from normal hepatocytes. The aims of the proposal are: 1) to identify the progenitor cell or new cell populations; and 2) to trace their evolution to the development of foci, hyperplastic nodules and hepatomas by a study of the acquired cellular or subcellular properties. Livers from chemical carcinogen-induced rat hepatoma models will be analyzed for various markers reported associated with persistent hyperplastic nodules that develop into hepatomas. These markers include: 1) distribution of enzymes increased in hyperplastic nodules (e.g., UDP-glucuronyltransferase, gamma glutamyltransferase, glutathione-S-transferase, epoxide hydrase); 2) distribution of surface membrane receptor (hepatic binding protein (HBP)); 3) detection of hepatocyte-specific mRNA sequences (e.g. alpha - fetoprotein, UDPG-transferase, HBP); and 4) detection of oncogenes (e.g., fos, c-myc, H-ras, K-ras, etc.) expressed in cell proliferation or transformation. Markers will be analyzed for their distribution to intracellular membrane compartments that comprise endocytotic, biosynthetic, secretory, glycosylation, sorting or degradative pathways. This analysis will determine if cellular phenotypic changes are coincident with functional changes in the membrane compartments. The methodologies to be employed are enzyme/immunocytochemistry, in situ cDNA hybridization and ultrastructure.